The present invention relates to a technique for detecting a misfiring in an internal-combustion engine.
The Japanese Patent Application Publication No. H3-246374 discloses a technique for estimating a movement of a motoring pressure (a pressure at a misfiring time) of an engine by detecting an internal pressure of a combustion chamber of the engine for each predetermined crank angle, setting a bias amount of an internal pressure detection signal based on an internal pressure detection signal sampled in a sampling period and a volume of the combustion chamber, correcting the sampled internal pressure detection signal based on the set bias amount and estimating the movement of the motoring pressure based on the corrected internal pressure and the combustion chamber volume. An occurrence or no occurrence of misfiring is determined by comparing this estimated pressure with the detected pressure in a combustion cycle.
According to the above-described conventional technique, the internal pressure is first obtained by correcting the internal pressure signal with the bias amount and then the motoring pressure is estimated based on the corrected internal pressure and the combustion chamber volume. However, this technique has a weak point in reliability for correcting the detected pressure value with the bias amount because the detected pressure is corrected with the bias amount at a certain time point when the internal pressure changes abruptly under a transient operation of the engine and because the characteristic of the output of the internal pressure varies due to such several factors as the sensor attachment state, change of temperatures at the sensor attachment portion, aging deterioration and so on. Therefore, there is a need for improving reliability of the motoring pressure that is estimated from such corrected pressure value.